A U.S. company with political connections to the White House says it may have overcharged the Pentagon by some $6 million for work in Iraq. The disclosure was made by the energy giant Halliburton, which was once headed by Vice President Dick Cheney.

Houston-based Halliburton says its own internal audit caught a $6 million potential overbilling by one of its subcontractors for work in Iraq, where the company already has reconstruction and military projects worth billions of dollars.

At least one person allegedly involved in kickbacks is now said to have left the Halliburton subsidiary, Kellogg, Brown and Root. The Pentagon has refused comment on the matter but the issue has been forwarded to the Defense Department's inspector general for possible investigation.

Halliburton has already come under fire, especially from Democrats, who charge it has been awarded contracts in Iraq because of its close ties to the White House through Vice President Cheney, who led the energy giant until 2000. Halliburton denies receiving preferential treatment and is promising to repay any questionable charges to the government. But some Senate Democrats say it's now time for a formal investigation.